1. Field of the Invention
The invention relates to a process for preparing D-pantothenic acid using Coryneform bacteria in which the poxB gene is attenuated.
2. Discussion of the Background
Pantothenic acid is a vitamin of commercial importance, which is can be used in human medicine, pharmaceuticals, foodstuffs industry and particularly in animal nutrition. Pantothenic acid can be prepared by chemical synthesis, or biotechnologically by fermentation of suitable microorganisms in suitable nutrient solutions. In the chemical synthesis, DL-pantolactone is an important intermediate stage. It is prepared in a multi-stage process from formaldehyde, isobutylaldehyde and cyanide. In further process steps, the racemic mixture is separated, D-pantolactone is subjected to a condensation reaction with β-alanine, and the desired D-pantothenic acid is obtained in this way.
The advantage of the fermentative preparation by microorganisms lies in the direct formation of the desired stereoisomeric D-form, which is free from L-pantothenic acid.
Various types of bacteria, e.g. Escherichia coli (E. coli), Arthrobacter ureafaciens, Corynebacterium erythrogenes, Brevibacterium ammoniagenes, and also yeasts, e.g. Debaromyces castellii, can produce D-pantothenic acid in a nutrient solution which comprises glucose, DL-pantoic acid and β-alanine, as shown in EP-A 0 493 060. EP-A 0 493 060 further shows that in the case of E. coli, the formation of D-pantothenic acid is improved by amplification of pantothenic acid biosynthesis genes from E. coli which are contained on the plasmids pFV3 and pFV5 in a nutrient solution comprising glucose, DL-pantoic acid and β-alanine.
EP-A 0 590 857 and U.S. Pat. No. 5,518,906 describe mutants derived from E. coli strain IF3547, such as FV5714, FV525, FV814, FV521, FV221, FV6051 and FV5069, which carry resistances to various antimetabolites, such as salicylic acid, α-ketobutyric acid, β-hydroxyaspartic acid, O-methylthreonine and α-ketoisovaleric acid. They produce pantoic acid in a nutrient solution comprising glucose, and D-pantothenic acid in a nutrient solution comprising glucose and β-alanine. It is further shown in EP-A 0 590 857 and U.S. Pat. No. 5,518,906 that after amplification of the pantothenic acid biosynthesis genes contained on the plasmid pFV31, in the above-mentioned strains the production of D-pantoic acid in nutrient solutions comprising glucose and the production of D-pantothenic acid in a nutrient solution comprising glucose and β-alanine is improved.
Processes for the preparation of D-pantothenic acid with the aid of Corynebacterium glutamicum (C. glutamicum) are known only in some instances in the literature. Sahm and Eggeling (Applied and Environmental Microbiology 65(5), 1973-1979 (1999)) thus report on the influence of over-expression of the panB and panC genes and Dusch et al. (Applied and Environmental Microbiology 65(4), 1530-1539 (1999)) report on the influence of the panD gene on the formation of D-pantothenic acid.
However, there remains a need for improved methods of producing pantothenic acid in Coryneform bacteria. On a commercial or industrial scale even small improvements in the yield of pantothenic acid, or the efficiency of their production, are economically significant. Prior to the present invention, it was not recognized that attenuation of the poxB gene in Coryneform bacteria would improve pantothenic acid yields.